2/23/2010R. Munden - Fairfield University1.  Discuss the makeup of an electromagnetic wave and the characteristics of an isotropic point source  Explain.

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Presentation on theme: "2/23/2010R. Munden - Fairfield University1.  Discuss the makeup of an electromagnetic wave and the characteristics of an isotropic point source  Explain."— Presentation transcript:

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2/23/2010R. Munden - Fairfield University1

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 Discuss the makeup of an electromagnetic wave and the characteristics of an isotropic point source  Explain the processes of wave reflection, refraction, and diffraction  Describe ground- and space-wave propagation and calculate the ghosting effect in TV reception  Calculate the approximate radio horizon based on antenna height  Discuss the effects of the ionosphere on sky-wave propagation  Describe the important aspects of satellite communication  Define the importance of figure of merit and link budget analysis

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 Transducers convert energy between forms  To send signals through the air, Electricity is converted into Electromagnetic energy by the antenna  Light and RF are both EM waves, only the frequency is different  You can compare a radio wave emitted or detected by an antenna to a photon emitted by an LED and detected by a photodiode

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Electric currents excite magnetic fields. This energy can be radiated out as an electromagnetic wave, a transverse wave where electric and magnetic fields are perpendicular to each other. The direction of propagation is perpendicular to both. The polarization is in the direction of the E field

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Power at wavefront Electric Field Power relates to characteristic impedance, like Ohm’s Law Spherical wavefronts from isotropic point source

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 Electromagnetic waves obey all the laws of optics.  Radio waves are really no different than light, except that the frequency is much lower, and the wavelength much longer.

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1. Ground Wave 2. Space Wave 3. Sky Wave 4. Satellite Communications Frequency of the radio wave is the most important aspect when comparing the different types of propagation

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 A vertically polarized EM wave propagates along the Earth’s surface  Effective over conductive surfaces (like seawater)  Only good to 2MHz, but are very reliable  ELF ( Hz) is used to communicate with submerged submarines. One transmitter can be “felt” all over the globe. Clam Lake, WI: Project ELF (Seafarer), broadcast at 76 Hz using 30+ mile antenna. Requires it’s own power plant to drive.

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Roughly 50 mi range

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AM transmitted TV video signals can interfere with each other, creating a “double” or “ghost” image when the signal reflects off of the ground or another object

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The Sky has three zones: the Troposphere ( mi), Stratosphere (6.5 – 23 mi), and Ionosphere (23 – 250 mi). Radio waves can be “bounced” between the ionosphere and the ground to achieve long distance communications

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Geosynchronous orbit at 22,300 miles above the equator. Acts as a transponder to receive and retransmit the signal from a terrestrial transmitter (the Uplink) to a terrestrial receiver (the Downlink)

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LEO satellites (between miles altitude) have short delay (5-10ms) Cheaper launch, but a constellation of satellites is necessary to cover the whole earth. Coordination between several satellites to hand-off communications as they orbit

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 To find the look angle of a terrestrial receiver or transmitter. For Elevation For Azimuth E = elevation in degrees A = azimuth of the antenna S = satellite longitude N = site longitude G = S-N L = site latitude

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Satellite can carry out communication with any earth stations within its footprint. May be designed with 2 footprints to conserve power Frequency Division Multiple Accses (FDMA) was originally used by satellites to allocate specific bands to transmitters as needed

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New satellites use TDMA to allow operation on only 1 frequency. Use is allocated to data bursts which allow multiple users to communicate. Very compatible with current digital technology, easily allows demand based multiplexing.